/Engine/Source/Runtime/SlateCore/Public/Widgets/SWidget.h
Gets whether or not the specified users has this widget focused, and if so the type of focus.
The optional will be set with the focus cause, if unset this widget doesn't have focus.
[TOptional](API\Runtime\Core\IO\TOptional)< EFocusCause > HasUserFocus ( int32 UserIndex ) const